The effect of turbulence and shear on the flow around three dimensional square cylinders

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Abstract

The effect of turbulence and shear on the flow around square
cylinders has been investigated (i) for models without a free
end at incidence a in the range 00<a< 45 0 for models with
and without end plates and, (ii) for models with a free end
at a=00 and a= 45 0 for model height H to width D ratio
H/D in the range 2 :5 H/D 5 11. The Reynolds number, based on
4
the model width was 4.8 x 10
It has been found that end plates are necessary to simulate a
two dimensional flow condition in uniform smooth flow provided
the wall boundary layer is greater than about 10% of the model
span. In other uniform flow conditions, away from the wall
boundary layer affected region, which is about the physical
thickness of the boundary layer, two dimensionality could be
assumed. In linear shear flow., end plates reduced the base
pressure in the low velocity region. Two dimensional model
results agree well with the published results.
Finite square cross-section cylinders exhibit a free end
region of length ZF and a root region. Three regimes, Low H/D,
Middle H/D and High H/D are found in all flow conditions. The
drag on the finite cylinder in smooth flow is lower than that
in turbulent flows. Provided the flow is turbulent, increasing
turbulence decreases the drag. For a particular flow
condition, increasing H/D ratio increases the drag.
It appears that in the high H/D regime there is a shedding of
the free end eddy. The shedding frequency is lower than the
shedding frequency in the root region of the cylinder.
The effect of shear can be ascertained by correcting the flow
results for the local velocity and thus shear need not be
considered a critical flow simulation parameter.